1. Field of the Invention
This invention relates to a solenoid valve used to control the pressures of various kinds of fluids.
2. Description of the Related Art
The conventional art solenoid valves of this kind include, for example, a solenoid valve shown in FIG. 3. FIG. 3 is a sectioned schematic construction diagram of this conventional art solenoid valve.
A solenoid valve 101 includes a solenoid portion 102 and a valve portion 103.
Here, in the illustrated example, the valve portion 103 is a spool valve. In the interior of a valve sleeve 131, a spool 132 is provided so that the spool 132 can be reciprocatingly moved. Since a cross-sectional area of an opening of a valve formed in the valve sleeve 131 varies in accordance with a stroke of the spool 132, an inflow rate and an outflow rate of a fluid can be controlled through a control operation for a quantity of a stroke of the spool 132 by the solenoid portion 102.
The solenoid portion 102 is provided with a substantially cylindrical coil 121 adapted to generate a magnetic field when it is energized thereto, a movable plunger 122, a center post 123 adapted to magnetically attract the plunger 122 thereto when a magnetic path is formed by a magnetic field occurring owing to energizing the coil 121, and a rod 124 connected to the plunger 122 so as to transmit a driving force of the plunger 122 to the spool 132.
The solenoid portion 102 is further provided with a substantially bottomed cylindrical metal sleeve 125 packed with the plunger 122, opened at one end thereof which constitutes a bearing for the plunger 122, and closed at the other end thereof, an upper plate 126 interposed between the coil 121 and sleeve 125, and a bracket 127 having a mounting portion 127a to a predetermined portion of which a body of the solenoid valve 1 is fixed.
Next to the closed end of the sleeve 125, a connector 128 is provided which has a terminal 128a connected to the coil 121 via an electric wire 121a, so as to supply electric power to the coil 121.
A case member 129 is provided which houses therein various constituent members including the coil 121, plunger 122, center post 123, sleeve 125, bracket 127 and connector 128.
Furthermore, the solenoid portion 102 is provided with a bobbin 140 around which the coil 121 is wound, a shim 141 for rendering the plunger 122 easily separable from the center post 123, and a bearing 142 for the rod 124.
On the other hand, the valve portion 103 side is provided with a spring 134 which urges a metal member 133 fixed to the spool 132, in the direction in which the plunger 122 is separated with the spool 132 from the center post 123 via the rod 124.
The coil 121 and bobbin 140 are molded into one part to constitute a molded coil subassembly for the solenoid valve 101.
The solenoid valve 101 shown in FIG. 3 is so formed that a collar portion 125a is provided at an open end of the sleeve 125 so as to extend to a position near an inner circumferential surface of the case member 129. The collar portion 125a is curved in a position close to the bracket 127 to form a stepped portion, the collar portion 125a being then separated from the bracket 127 and extended in the radially outward direction. The collar portion 125a, bracket 127 and the inner circumferential surface of the case member 129 define a substantially annular space 150.
In this annular space 150, a seal member 104 is provided. The seal member 104 prevents the leakage of a fluid from the interior of the valve portion 103 into a region in which the coil 121 and connector 128 are provided, and the entry from the outside thereinto of contaminant, such as water which causes poor insulation or short-circuiting of the coil 121.
The operation of the solenoid valve 101 will now be described.
The plunger 122 is in a position away from the center post 123 in a normal condition, i.e., in the condition in which the coil 121 is not energized. During this time, the metal member 133 is urged by a spring 134 to cause the spool 132 to be pressed toward the solenoid portion 102. As a result, the rod 124 is forced into the solenoid portion 102, so that the plunger 122 is separated from the center post 123.
When the coil 121 is energized, a magnetic path (formed by the case member 129, upper plate 126, plunger 122, center post 123 and bracket 127) is formed around the coil 121, and the plunger 122 is magnetically attracted to the center post 123 against the urging force of the spring 134.
Therefore, the magnetic force is controlled in accordance with the level of an electric current supplied to the coil 121 and a flow rate of a fluid is thereby regulated by controlling a quantity of a stroke of the spool 132 on the basis of a quantity of movement of the plunger 122. The controlling of pressures of various kinds of fluids, such as the controlling of a hydraulic pressure is done in this manner.